Cathode ray tube gun structure



Sept. 22, 1959 Filed Oct. 18, 1957 60/E00/V E. SPENCER United SttesCATHODE'RAY TUBE GUN STRUCTURE Application October 18, 1957,'Serial No.691,026

.Claims. (Cl.'313-82) This invention relates ,generally to electrondischarge devices, and more particularly to improved electrode mountingmeans associated therewith.

Conventional cathode ray tubes generally employ an electron gun assemblyhaving a plurality of tubular electrodes mounted in spaced relationalong a common axis, the assembly typically including a tubularfilamentary type cathode, a control grid, an accelerating screen gridelectrode and a high voltage anode, the entire gun structure beingmounted in the neck portion of a cathode ray tube envelope.

The type of cathode employed in such tubes is of the indirectly-heated,oxide-coated variety, consisting of a small metal tube closed at oneend, usually made of nickel or a nickel alloy, and having on the outersurface of the closed end a deposit of electron emissive material, thematerial being heated, during tube operation, to thermionic temperaturesby a helically wound filament or heater inserted within the cathodesleeve.

Cathode ray tube gun structures made in accordance with standardpractice and embodying the general arrangement of electrodes discussedabove have been found generally satisfactory. There are, however,certain disadvantages inherent in this type of electrode gun struc ture.These disadvantages, or limitations, are particularly manifest in fieldsof application where compactness and low power consumption are ofprincipal concern, as for example, in the manufacture of portabletelevision apparatus.

The cathode normally employed in cathode ray tubes, consumesconsiderable power during operation. Thisis principally brought about bythe fact that the electron emitting surface of the cathode must bebrought to thermionic temperatures by heat conducted to it through thecylindrical walls of the tubular cathode. This mode of operation,results in considerable waste of energy through both radiation to coolersurroundings and conduction away from the cathode through the supportingstructure associated therewith. This thermally ineflicient arrangementresults in a considerable loss of power from the tube system and isparticularly objectionable, as indicated above, in situations whereminimum power consumption is a primary consideration. Moreover, thethermal inetficiency of this type cathode construction is accentuated bythe fact that to provide sufiicient cathode end area on which to depositthe requisite amount of electron emissive material necessitates acathode sleeve of relatively large diameter. This requirement gives riseto use of a cathode having an extensive surface area, a configurationpoorly adapted to this type of operation and one whose losses throughradiation are excessive. To supply this type cathode with sufficientpower to actuate the electron emissive material requires a heaterfilament of considerable lengthand consequently a cathode of suflicientdepth .to receive it, thereby materially increasing the overall lengthof the cathode ray tube gun structure.

atent Another objectionable feature, arising out of the concentric.telescoping arrangement of the cathode and control grid, is thenecessity of using a plurality of auxiliary members to bring aboutacceptable interelectrode'alignment. To keep the accumulated error ofsuch a composite assembly within acceptable limits requires that thecomponent parts be dimensioned to exceedingly close tolerances. Thistechnique, while producing an acceptable product, isboth expensive andtime consuming.

Moreover, accurate axial spacing between the cathode and grid, incontradistinction to axial alignment, is additionally complicated by thefact that the thermal gradients, induced by thermionic heating of thecathode element in the manner discussed, produce corresponding changesin the cathodes length affecting its spacing from the control grid. Thisvariation in spacing results in'a fluctuating cross-over point adverselyaffecting spot size.

In addition to proper .cathode-to-grid spacing .it is equally importantto the proper functioning of the cathode ray tube, that the electronbeam apertures of the control grid and its immediately adjacentaccelerating electrode be in precise axial alignment. Any deviation fromtrue alignment results in a condition known as coma, seriously impairingthe efiectiveness of the electron optical focusing system. Theconventional arrangement of electrodes does not admit of a simple methodof electrode alignment but on the contrary requires elaborate jigging toobtainthe registration necessary to insure acceptable focusing of theelectron Writing beam.

In the television art in general there has been .an increasing demandfor more compact television picture tubes of larger fluorescent screenarea. This trend, while predicated .in large degree on aesthetics hascertain more tangible causes, one of which is the production of acheaper television set through decrease in the .size of the requiredtelevision cabinet and other complementary equipment. Attempts tocompress the overall length of the conventional gun assembly, in orderto reduce costs and create a more aesthetically pleasing product have todate been largely unsuccessful.

It is accordingly an object of the invention toprovide a cathode raytube gun structure of considerably shorter length than conventionalassemblies, thereby permitting the fabrication of a more compact cathoderay tube.

It is another object of this invention to providea unique cathode raytube gun structure facilitating the alignment of the electron beamapertures of the control grid and first accelerating electrode.

It is a general object of this invention to provide a novel electrodemounting structure which overcomes the limitations of prior art devices.

The aforesaid and other objects within contemplation will be morereadily understood by reference to the following detailed descriptionand drawing, in which:

Figure 1 is a fragmentary elevational view of the neck portion of acathode ray tube embodying structure of the present invention;

Figure 2 is an exploded view of a portion of the gun assembly depictingthe interrelation of the parts;

Figure 3 is a perspective showing of the compactly integrated electrodeassembly;

Figure 4 is an illustration of one form of apparatus adapted for use inbringing about axial alignment of the electron beam. apertures; and

Figure 5 is a phantom showing of the cathode-grid module depictingcertain structural innovations.

This invention, stated generally, relates to novel electro'cle mountingmeans facilitating precise interelectrode registration and permittingthe incorporation, within a cathode ray tube, of a cathode disposed in aplane transverse the tube axis. The accurate spacing required betweencathode and control grid is insured by the simple expedient of insertingthe cathode sleeve and pre-formed vtab portions of a box-like grid intosuitable aligned apertures punched in sheet-like insulating supportmembers .design still further provides means for varying tubetransconductance through a unique method of grid spacing.

Still another aspect of this invention relates to means for axiallyaligning the electron beam apertures of the control grid and firstaccelerating electrode (screen grid). This is accomplished in a mannerunique to the television art and comprises punching a set of orientingholes, conveniently of equal diameter, into the electron beam aperturedplate of each electrode, the hole pattern in each case being identicallypositioned in relation to its respective electron beam aperture.

This technique facilitates a simplified assembling procedure, whichconsist of merely slipping the orienting holes of each member overappropriately disposed prongs of suitable diameter which serve to impalethe members in precise registration. To insure minimal deviation fromtrue axial alignment the orienting prongs may be slightly tapered inorder to compensate for slight deviations in the diameter of theorienting holes. Once located, the electrodes are maintained in preciseoriented relation by being joined to the cathode-control grid module, asfor example by spot welding.

Now making detailed reference to the drawing, Figure 1 shows a cathoderay tube gun assembly 9 comprising a high voltage anode 10, screen grid11, and the cathodecontrol grid module 12, the high voltage electrodes10 and 11 being mounted in conventional fashion on the glass beading 13.This invention relates to unique electrode mounting structure comprisingthe screen grid 11 and its cathode-control grid appendage 12.

To facilitate a clearer understanding of this composite assembly theexploded perspective shown in Figure 2 has been employed, which inconjunction with Figure 3 clearly depicts the relative disposition andinterrelation of the parts of the assembly.

This assembly comprises the insulating mica support members or plates 14disposed in parallel spaced relation and adapted to support, by means ofsuitable positioned apertures, a tubular cathode 15, a box-like controlgrid 16, and channel shaped side rails 17. To aid in installing thecathode, the tubular sleeve is dimpled in regions 18 and 19, theseprominences serving to provide a locating stop when inserting thecathode into the supporting aperture 20. The cathode is retained in thisoriented position by later spot welding a conductor strap 21 to thatportion 22 of the cathode sleeve projecting beyond the outer surface ofthe mica support member 14, the cathode when completely installed beingfreely suspended between the mica support members 14 in a planetransverse the electron beam axis of the cathode ray tube. The cathodeis aligned in back of the grid aperture 23, with the electron emittingsurface 24- of the cathode in confronting relation thereto. Embracingthe cathode is the box-like control grid 16, this member being locatedin accurate spaced relation to the cathode by positioning the gridlocating tabs 25 within their respective mating apertures 26 in theinsulating support members 14. This structure is desirably of box-likeconfiguration to increase its structural rigidity. Moreover, because ofthe tendency of the knife-like edge portions of the tabs to cut into themica support, it is desirable, in order to prevent dislocation of thegrid structure, to have flat portions of the positioning tabs 25 and 25ain spaced opposed relation as shown in Figure 3. The preferred box-likeconfiguration of the control grid conveniently provides this desiredorientation of tab members.

Bounding the control grid 16, but electrically insulated therefrom, arethe side rails 17, these members preferably being made of electricallyconductive material and supported by the mica members 14 in a mannersimilar to that described for the control grid 16. By the simpleexpedient of bending or off-setting certain of the locating tabs 28, toprevent their withdrawal from the mica support plate 14, these membersserve to lock the assembly into a composite unitary structure. The siderails are then joined to the screen grid 11, as by spot welding, afteralignment of the electron beam apertures by means hereinafter described.

The spacer plate 27 facilitates juncture of the cathodecontrolgrid-module to the screen grid. electrode and also provides accurate,simplified means for varying the spacing between the screen and controlgrids thereby providing a convenient method of varying tubetransconductance. This plate is desirably configured to bridge themodular assembly in such manner that the screen grid 11, on which theplate is mounted, as by spot welding is suspended from the upper flanges29 of the side rails 17, in spaced relation to the control grid 16, theaxial spacing between these members being accurately determined by thethickness of the spacer plate 27.

The next step in fabricating the electrode assembly is to bring theelectron beam apertures 23 of the screen grid 11 and control grid 16into precise axial alignment.-

7 Both these members are provided with orienting holes 30 punched intotheir confronting surfaces, these holes preferably being punched by thesame die used in piercing the electron beam apertures. The box-like gridstructure 16 has an additional pair of holes 31, shown in Figure 5,punched in its lower surface 32 to facilitate insertion of the orientingprongs 33 into and through the box-like structure. A preferred method ofassembly is to first position the module 12 on the orienting prongs 33in the manner shown in Figure 4, followed by similar impalement of thescreen grid 11. -Once positioned on the orienting prongs 33 the electronbeam apertures 23 are automatically brought into alignment. With themembers thus aligned the spacer plate 27 is spot welded to the flanges29, producing a composite unitary electrode assembly. Screen grid 11,prior to alignment of the control grid 16, may be conveniently staked,along with the high voltage anode 10, to the insulating beads 13, thecathode-grid module being subsequently appended to this high voltageelectrode assembly in the manner described.

The orienting prongs 33, in order to insure proper alignment, should beof sufficient thickness to resist distortion during assembly. Thisrequirement dictates the diameter of the orienting holes and oftennecessitates the use of a relatively large size hole as compared to thediameter of the electron beam aperture. Under certain tube operatingconditions electron leakage through these holes results in poor picturedefinition and in severe cases produces what is knownrin the televisionart as ghosts. To prevent this phenomenon, orienting hole shields 34, ofthe general configuration shown in Figure 5 may be employed. Theseshields are mounted against the inner surface 35 of the control gridside walls and effectively insulate the orienting holes 30 and accessholes 31 from the electron stream while permitting full utilization ofthe holes for purposes of orientation. This shielding may of course beaccomplished in a number of ways, for example, by plugging the orientingholes after assembly, but the most satisfactory technique, from thestandpoint of both cost and ease of assembly, is that described. 3 a gIt has been found expedient in certain applications, from both thestandpoint of structural stability and ease of making electricalconnections to the electrode assembly, to employ a reenforcing strap 35(Figure 5) positioned against the under surface of the assembly 112. Thestrap is spot welded to the side rails 17 and maintained in spacedrelation to the control grid 16, the upstanding terminal portions 36providing convenient means for electrically connecting the screen grid13 to the connecting pins 13, in the manner clearly shown in Figure 1.

While a preferred embodiment, illustrative of the apparatus of thepresent invention has been depicted and described, modifications may bemade therein Without departing from the scope of the present invention.It will be understood, therefore, that such changes and modificationsare contemplated as come within the purview of the appended claims.

I claim:

1. In cathode ray tube gun structure, a pair of sheetlike supportmembers of electrically insulative material having pre-punched aperturesin which an array of electrode elements are supported in predeterminedfixed orientation, said array including an elongated cathode elementdisposed transverse the electron beam axis of said structure; anelectroniapertured, box-like control grid encircling said cathodeelement; and a pair of spaced electrically conductive side railsinsulated from said cathode element and grid, said side rails spanningsaid sheet-like members and having end portions mounted in the latter,and said side rails forming an interconnecting bridge between thementioned cathode-grid assembly and accelerating high voltage electrodemeans, said high voltage electrode means being carried by said siderails in spaced confronting relation to said grid to form a rigid,unitary gun structure of reduced length Whose intere'lectrode spacing isfixed by said apertured support members.

2. In cathode ray tube gun structure, a pair of sheetlike supportmembers of electrically insulative material having pre-punched aperturesin which an array of electrode elements are supported in predeterminedfixed orientation, said array including an elongated cathode elementdisposed transverse the electron beam axis of said structure; anelectron-apertured, box-like control grid encircling said cathodeelement; and a pair of electrically conductive, generally C-shaped siderails insulated firom said cathode element and grid and forming aninterconnecting bridge between the mentioned cathode-grid assembly andaccelerating high voltage electrode means, said high voltage electrodemeans including a spacer plate fixedly attached to side rails and spacedin confronting relation to said grid to form a rigid, unitary gunstructure of reduced length Whose interelectrode spacing is fixed bysaid apertured support members.

3. In cathode ray tube gun structure, a pair of sheetlike supportmembers of electrically insulative material containing a pro-punchedpattern of apertures captively supporting an array of electrode elementsin predetermined, fixed alignment, said array comprising: a tubularcathode sleeve disposed in a plane transverse the electron beam axis ofsaid structure; an electron-apertured, box-1ike control grid encirclingsaid cathode sleeve,

spaced therefrom and electrically shielding said cathode from extraneouspositive voltage gradients; and a pair of electrically conductivechannel members flanking said grid and cathode, insulated therefrom andbridged by a centrally apentured, electrically conductive, plate-like,electrodeespacmg member on which there is mounted an acceleratingelectrode having a centrally cup-shaped portion extending through saidcentral aperture into confronting spaced relation with said grid, thecomposite assembly forming an extremely compact, unitary electron gunstructure in which interelectrode spacing is rigidly fixed by saidpie-punched support members.

4. In cathode ray tube structure, a pair of sheetlike support members ofelectrically insulative material having pro-punched apertures in whichan array of electrode elements are supported in predetermined fixedorientation, said array including an elongated cathode element disposedtransverse the electron beam axis of said structure; anelectron-apertured, box-like control grid encircling said cathodeelement; and a pair of electrically conductive side rails insulated fromsaid cathode element and grid and forming an interconnecting bridgebetween the mentioned cathode-grid assembly and an accelerating highvoltage electrode, said high voltage electrode being mounted on aseparately formed electrically conductive plate-like member carried bysaid side rails and supporting said electrode in spaced confrontingrelation to said grid to form a rigid, unitary gun structure of reducedlength whose interelectrode spacing is fixed by said apertured supportmembers.

5. In cathode ray tube gun structure, a pair of sheetlike supportmembers of electrically insulative material having pre-punched aperturesin Which an array of electrode elements are supported in predeterminedfixed orientation, said array including an elongated cathode elementdisposed transverse the electron beam axis of said structure; anelectron-apertured, box-like control grid encircling said cathodeelement; and a pair of electrically conductive side rails insulated fromsaid cathode element and grid and forming an interconnecting bridgebetween the mentioned cathode grid assembly and an accelerating highvoltage electrode, said high voltage electrode being anchored to anelectrically conductive plate-like member secured to said side rails andsupporting said electrode in spaced confronting relation to said grid toform a rigid, unitary gun structure of reduced length whoseinterelectrode spacing is fixed by said apertured support members.

References Cited in the file of this patent UNITED STATES PATENTS2,174,853 Bowie Oct. 3, 1939 2,508,979 Van Gessel May 23, 1950 2,608,744Starre et al. Sept. 2, 1952 2,728,007 Van Ormer Dec. 20, 1955 2,773,212Hall Dec. 4, 1956 FOREIGN PATENTS 707,064 Great Britain Apr. 14, 1954753,507 Great Britain July 25, 1956

